Over the years, a variety of power or energy sources operating off of heat derived from the oxidation of metallic lithium have been proposed. See, for example, U.S. Pat. No. 3,329,957 issued July 4, 1967 to Rose. In such a system, water and lithium are reacted to produce lithium hydroxide, hydrogen and steam. Elsewhere in the system, the hydrogen generated by the reaction between lithium and water is combined with oxygen to provide additional steam. The steam is then utilized to drive a turbine or the like to provide a source of power.
Other proposals have been made wherein lithium is oxidized for the purpose of providing heat in nonspecific environments. Examples may be found in Camp et al U.S. Pat. No. 3,156,595 issued Nov. 10, 1964 and Biermann U.S. Pat. No. 3,963,541 issued June 15, 1976. These proposals utilize lithium and/or lithium alloys as a fuel which is oxidized by sulfur hexafluoride. According to Biermann, lithium powder of a very small size is coated with a perhalogenated compound prior to being oxidized with sulfur hexafluoride.
More recently, systems have been proposed wherein metallic lithium, in the solid phase and as a generally solid block, is placed within an oxidation chamber of a boiler. When power is desired, the lithium is melted and oxidized with sulfur hexafluoride. The resultant heat vaporizes a working fluid, typically water, in a working fluid chamber in heat exchange relation with the oxidation chamber of the boiler. Again, a turbine may be driven by the working fluid.
While such a system is effective, it is not without its drawbacks. Typically, the system start is initiated by firing a thermal starting device which includes aluminum potassium perchlorate. The intention is to heat the thermal mass of the boiler and the lithium fuel therein to operating temperature and to this end, the aluminum potassium perchlorate generates extremely high temperatures, typically in the range of 5,400.degree.-8,500.degree. F. Substantial pressures may be generated during the ignition of the aluminum potassium perchlorate requiring high strength in the boiler structure. Furthermore, the aluminum potassium perchlorate, should it contact boiler surfaces or sulfur hexafluoride injection nozzles, can burn through the same resulting in system damage.
In the commonly assigned applications of Buford, respectively U.S. Ser. No. 618,893 filed June 8, 1984 , U.S. Pat. No. 4,634,479 and entitled "Power Source Utilizing Encapsulated Lithium Pellets and Method of Making Such Pellets" and U.S. application Ser. No. 733,049 filed May 13, 1985 U.S. Pat. No. 4,671,211 and bearing the same title, the details of which are herein incorporated by reference, to the various difficulties presented by the various prior art approaches mentioned previously are dealt with by utilizing metallic lithium in shot shape and size or spherical form. Such lithium pellets are coated with a predominantly fluorine substituted, perhalogenated polymeric material and are ultimately oxidized with sulfur hexafluoride. These components eliminate any need for aluminum potassium perchlorate starters and the attendant problems. Moreover, by appropriately selecting the size of the pellets, the ullage or void volume within the oxidation chamber can be controlled so as to readily accommodate the expansion of the lithium metal that occurs as the progression of the reaction raises the temperature of the lithium from the ambient to an elevated temperature.
At the same time, however, the coating of the lithium pellets with polymer is not an inexpensive procedure, nor is the formation of metallic lithium into pellets since there is no known concurrent need in other areas for lithium pellets.
The present invention is directed to overcoming one or more of the above problems.